All of us know that talking on phone impairs our driving but a new study has claimed that the reverse is also true as drivers lose about 20 per cent of their ability to comprehend and use language.

The study by researchers at the University of Illinois that appeared in the journal Psychonomic Bulletin and Review found that driving impairs language skills and the driver’s ability to remember and retell a story declines significantly while he is on the wheels.

“Two previous studies had reported that driving did not impair the accuracy and comprehension of speech but those findings made no sense to people like us who have studied language,” said senior author Gary Dell.

“You might think that talking is an easy thing to do and that comprehending language is easy. But it’s not. Speech production and speech comprehension are attention-demanding activities and so they ought to compete with other tasks that require your attention — like driving,” Mr. Dell said.

The new study was conducted in a driving simulator at the Beckman Institute for Advanced Science and Technology at Illinois.

The participants worked in pairs — one as a driver and the other as a conversation partner who was either in the simulator with the driver or talking with the driver via a hands-free cell phone from a remote location.

As the researchers expected, a participant’s ability to remember and retell a story declined significantly if he or she was also driving during the exercise. In contrast to their performance while sitting still, Mr. Dell said, “the drivers remembered 20 per cent less of what was told to them when they were driving.”

Declines in the accuracy of retelling the stories were most pronounced while drivers navigated through intersections or encountered more demanding traffic conditions. “This study shows that various aspects of language go to hell when you’re driving,” said psychology professor Art Kramer, who collaborated on the study.

The study reflects the tradeoffs that occur when people try to communicate while performing other tasks, Mr. Dell said. “The relative balance of attention to any two tasks is going to vary,” he said.

“And perhaps we don’t understand one another as well as we should because of this. With modern technology, we’re talking more and more while we are doing other things, but we may be understanding one another less and less.”